The invention pertains to a variable epi-illumination interference attachment according to Mirau for observation and measurement of object surfaces. Among the interference microscopy procedures that produce information on the micro structure of objects by utilizing the appearances of light interference patterns are the multi-ray interference equipment according to Tolansky as well as two-ray interference installations according to Michelson or Mirau.
An epi-illumination interference microscope according to Mirau is known from K. Mxc3xcze""s ABC der Optik, published by Werner Dausien, Hanau 1960, pages 400 and 401 (compare page 401, right column, in connection with FIG. 2). The design of this epi-illumination interference microscope contains a beam splitter between the front lens of an epi-illumination objective and the object to be examined. Furthermore, the side of the front lens facing the object has a mirrored spot in its central area. In this known arrangement, the incident illumination light is split into two parts at the beam splitter arranged orthogonally to the microscope""s axis. One part, an object beam, falls upon the object after passing through the beam splitter, is reflected there, and again passes through the beam splitter in order to finally re-enter the front lens of the objective. The other part, a reference beam, is reflected at the beam splitter, comes upon the mirrored spot, is subsequently reflected back onto the beam splitter and, after yet another reflection at the beam splitter, interferes with the object beam.
The disadvantage of this familiar set up consists, among others, in the fact that the objects to be examined can show reflection values that vary within wide margins. If, for instance, an object with a reflection value of only five percent is to be measured (e.g. a coal sample), one may encounter contrast problems, because the metallically reflecting mirrored spot shows, compared to the weakly reflecting coal sample, a very high reflection value. Contrast problems arise when the relative brightness between the reference beam and object beam is unbalanced, causing one beam to wash out the other, regardless of whether the beams interfere in a constructive or destructive relationship. If one beam is extremely bright and the other beam is extremely dim, the observer will be unable to determine whether the beams are interfering constructively or destructively.
It is thus the object of this invention to provide an epi-illuminating interference attachment with which surfaces of objects with very different reflection values can be observed and measured without any contrast problems. This particular interference attachment may thus be used without limitation for practically all objects in question. This invention accomplishes this. object regarding an interference attachment of the above mentioned type in part by attaching several beam splitters to a carrier. These beam splitters distinguish themselves definitively in their respective reflection/transmission characteristics. Depending on the reflection value of the object to be examined, a selected one of these beam splitters may be moved into working position. This object of the invention is also accomplished in part by providing exchangeable reference mirrors having distinct reflection values for selective inclusion into the attachment.
Additional suitable designs result from the claims below.